WO2013185983A1 - Refractory ceramic batch and brick produced therefrom - Google Patents

Description

 Refractory ceramic offset and stone formed from it

Description

The invention relates to a refractory ceramic offset and a refractory ceramic stone formed therefrom.

Refractory ceramic products can be divided into different categories, for example basic and non-basic products. The invention relates only to basic products, namely an offset and a stone whose basic base material consists of sintered magnesia and / or fused magnesia.

From DE 44 03 869 C2 and DE 198 59 372 C l generic offsets and stones are known. In addition to the basic basic material, the known products of spinels (Herzynit, Galaxit, Jacobsit). It was found that advantageous mechanical properties of the fired product can be achieved by combining the basic base material with said spinels.

In particular, the ductility (brittleness) of the fired shaped article is improved (reduced), in some cases also the resistance is improved, in particular against attack by alkalis.

It is mentioned that the reaction and sintering mechanisms are not fully clarified when the corresponding parts are burnt,

different findings, however, suggest that none

complete, dense sintering between the individual

In other words, although the offset components enter into a physicochemical interaction upon firing, the product is less brittle than the individual offset components and becomes "more elastic overall ".

Although the aforementioned refractory products have been proven in the industry for many years and for example for

Lining of cement rotary kilns are used, there is a desire for further improvements, in particular with regard to the thermal resistance of the fired products. For example, the invariant point in the system dicalcium silicate calcium aluminate spinel periclase is only about 1325 ° C. The invention has for its object to offer a basic refractory ceramic offset, from which can be produced refractory moldings, which in addition to an advantageous structural elasticity have a high fire resistance, which is determined by an invariant point over 1 .400 ° C. Preferably, the fired product should also have a particularly good corrosion resistance.

The invention leaves the way outlined in the prior art to employ spinels in combination with a periclase base material. It has been found that the Al ₂ O ₃ content of the spinels is essential for reducing the thermal stability of the fired products. This applies in particular in combination with the offset component CaO. Although the CaO content of the total offset can be reduced by using low-calcium base materials. However, the problem persists when calcium oxide is returned during use. This is for example in rotary kilns for the production of

Cement clinker the case.

Extensive tests have found that these disadvantages can be solved by a completely different offset component, namely an offset component from the group: silicon carbide,

Silicon oxycarbide, silicon oxycarbonitride, silicon nitride.

If a stone is pressed and fired from the offset, after addition of a customary binder such as lignosulfonate (for example in an amount of up to 4% by mass, based on the total offset) (in particular in the temperature range from 1 .400 ° C. to 1 .600 ° C.) it comes at a product according to the invention only to partial sintered bridges between the basic (MgO) base material and the granular aggregate, wherein in particular the following mineral phases form: MgSi0 ₃ , Mg ₂ Si0 ₄ , Si0 ₂ . Si0 _{2 is formed} by the oxidation of SiC during an (oxidizing) pyroprocess. In most cases, Si0 ₂ reacts with MgO to form enstatite. Adjacent to it forms forsterite, which establishes a direct bond to the basic basic material, since

Enstatite is not stable next to MgO.

It could be observed in experiments that a maximum of half of the surface of the granular aggregate is sintered with the surrounding refractory basic material. Often lies the grainy

Supplement after firing even loosely in the basic matrix, that is, there are no solid compounds between individual aggregate grains and the basic matrix material. In the direct

Surrounding the aggregate grains may occur in addition to MgO also forsterite. The extent of sintering of the granular aggregate with the

surrounding refractory basic material could be detected by a microscopic polished section investigation; It was found that the grain periphery is sintered for a maximum of half their length with the surrounding basic basic material.

In that regard, the microstructure of a refractory ceramic product of the present invention differs from a microstructure of a prior art brick containing spinel. With the new product at least the ductility characteristics are achieved, which are the well-known

Spinel products. In relation to this prior art, the product of the invention is characterized by a significantly increased invariant point regularly at least 100 ° C, often more than 200 ° C above that of

Products with Herzynit and / or Galaxit and / or Jacobsit lies.

The fire resistance is correspondingly high.

In the most general embodiment, the invention comprises a refractory ceramic batch of the following composition:

75 to 98 M.% of at least one basic basic material from the group: sintered magnesia, fused magnesia,

 2 to 25 M.% of at least one granular aggregate from the group: silicon carbide, silicon nitride, silicon oxycarbide,

 Siliziumoxicarbonitrid,

 maximum 5 m. -% other ingredients

 - where the mass information in each case on the total offset

 Respectively.

The abovementioned properties can be optimized by the following variations, which can be implemented individually and in combination with one another, unless this is expressly excluded:

Use of the basic basic material with a proportion of> 10 and <40% by mass (based on the total offset) in one

Flour fraction <125 μιη, Use of a basic basic material with a proportion of> 35 M .-% (based on the total offset) in a grain fraction> 1 mm,

 Use of the granular aggregate in a grain spectrum> 125 μιη and <3 mm, wherein the lower limit may also be> 0, 5 mm and the upper limit and <2 mm,

 Reduction of the aggregate fraction of the total offset to between 2 and 10% by mass,

 Selection of a basic basic material which itself consists of at least 95% by weight of MgO, this proportion preferably being even higher, for example above 97% by mass or above 98.5% by mass,

- Matching of grain sizes of aggregate and basic

 Base material such that the dcio value of the base granular base material (ie basic base material without the

 Flour fraction <125 μιη) above the dcio value of the granular

 Surcharge,

Use of a basic base material with an iron content, measured as Fe ₂ O ₃ , of less than 0.6% by mass, based on the basic base material, this proportion should be as low as possible, for example <0.3%. .

 Selection of the basic basic component in such a way that it contains little or no (in each case <0.3 mol%) chromium oxide and / or aluminum oxide, based on the total offset, and the aggregate should also be as pure as possible in order to obtain the

optimally achieve the desired effects, with extraneous components of the surcharge, in particular to <5% by mass, based on the mass fraction of the aggregate in the overall offset, are favorable. The offset according to the invention thus comprises in particular two

Offset components (basic basic material, granular aggregate) in different grain fractions, wherein it has proved to be advantageous if the basic base material has a share of a flour fraction (<125 μιη), while the granular aggregate predominantly (preferably at least 90%) in one Grain fraction outside (above, so in a coarser grain size) of this flour area should be present.

Apart from small amounts of impurities, which are mainly caused by the raw materials used, this contains

product according to the invention (in addition to the carbide and / or nitride of

Zuschlags) only the oxides CaO, MgO and Si0 ₂ . The ratio CaO / Si0 ₂ for the basic component used is correspondingly high and is preferably at least 2, in particular>3,> 4 or> 5. Thus, an invariant point of well over 1 .700 ° C can be achieved.

For the high CaO / Si0 ₂ ratio, the carbidic or nitridic bond of the silicon is also responsible. This also has advantages in terms of corrosion stress of the fired

Product.

In the case of the use of a silicon carbide, an oxidized pyrolytic process may lead to a partial oxidation of the silicon carbide, which leads to a reduced CaO / Si0 ₂ ratio. In this way, increased sintering would cause what

is in principle undesirable, because it would increase the brittleness. In that regard, the offset according to the invention makes it possible, however

Setting a specific ductility of the fired product by adjusting the furnace atmosphere during firing.

Finally, the invention allows impregnation of the fired products with carbon, for example pitch. This is not possible with prior art products (with spinel additions in the form of Herzynite, Jacobsite or Galaxite) because the spinels contain iron or manganese oxides which would be reduced at application temperatures by the infusion material. That would mean that

Oxidizing impregnating material and thus at least partially ineffective. In contrast, the product according to the invention is compatible with such a carbon impregnation, especially since it is substantially

Embodiments already contains a carbidic substance (the granular aggregate).

To produce the ceramic molding according to the invention, a binder is added to the offset. The binder can be added to the offset, for example in proportions in the range from 1 to 4% by mass, in particular also in proportions in the range from 2 to 3% by mass, in each case based on 100% by mass of the total offset (the proportions Binders add up to 100 M -% of the offset added).

The refractory ceramic molding according to the invention is characterized in its most general embodiment by the following features, in each case determined at room temperature: made from an offset of the type mentioned,

 subsequent pressing to a molding,

 subsequent fire at temperatures between 1,400 ° C and 1,600 ° C,

 the granular surcharge is a maximum of half with the

 sintered surrounding basic basic material.

The stone can then have the following characteristics:

Young's modulus: <60 GPa

 - Breaking work:> 200 Nm

 nominal notched tensile strength: <9 MPa

 characteristic length:> 250 mm

 - invariant point:> 1,700 ° C.

The modulus of elasticity (modulus of elasticity) can in particular be determined as described in the following reference: G. Robben, B. Bollen, A. Brebels, J. van Humbeeck, O. van der Beast: "Impulse excitation apparatus to measure resonant frequencies, elastic module and internal friction at room and high temperature ", Review of Scientific Instruments, Vol.68, pp.4511-4515 (1997).

The breaking work, the nominal notch tensile strength and the

In particular, characteristic length may be determined as described in the following reference: Harmuth H., Manhart Ch., Auer Th., Gruber D .: "Fracture Mechanical Characterization of

Refractories and Application for Assessment and Simulation of the Thermal Shock Behavior ", CFI Ceramic Forum International, Vol. 84, No. 9, p. E80 - E86 (2007).

The invariant point can in particular be determined from the

Phase system of the mineral phases present in the stone.

The stones can be used preferably in industrial furnaces such as rotary kilns for cement clinker production, but also in the steel industry.

Other features of the invention will become apparent from the features of the claims and the other application documents.

The invention will be explained in more detail below with reference to various embodiments.

Table 1 below shows four different refractory ceramic offsets, the offsets S-1, S-2 and S-3 representing embodiments of offsets according to the invention and offset S-0 indicating the composition of a comparative offset not according to the invention. All data on the shares of offsets in the respective components are in% (% by mass), relative to 100 m. -% of the total total offset. Offset component S-0 Sl S-2 S-3

Sintered magnesia 15.0 15.0 15.0 15.0 (grain fraction 3 to 5 mm)

 Sintered magnesia 40.0 37.0 36.0 34.0 (Grain fraction 1 to <3 mm)

 Sintered magnesia 15.7 13.9 13.1 12.2

(Grain fraction 0.125 to <1 mm)

 Sintered magnesia 29.3 29.1 28.9 28.8 (flour fraction <125 μιη)

 Silicon carbide 0 5 7 10

(Grain fraction 0.5 to 1.7 mm)

 Table 1

The manufacturing process for producing a stone according to the invention with the offset components according to Table 1 was in each case as follows:

Mixing of the offset components with the binder, namely 2.5 M .-% liquid lignosulfonate, based on 100 M .-% of the total offset,

 Pressing of normal stones (230 x 85 x 114 mm) with a pressure of 140 MPa,

 Burn the stones at 1,400 ° C in air for 8 hours.

The data and characteristics of the stones produced from the sets according to Table 1 are given in Table 2. The stones created from the offsets are each with the

Designations (S-0, S-1, S-2, S-3) of the corresponding offsets.

Further, in Table 2, for comparative purposes, the data and Characteristics of four other refractory bricks based on a basic base material shown, which are not created in each case with an inventive offset. Specifically, the stones AD are the following stone types:

A: Burnt magnesia brick based on sintered magnesia with 94 M .-% MgO and 6 M .-% Fe ₂ O ₃ .

B: Burnt magnesia based on sintered magnesia with 97 M .-% MgO, 2 wt .-% Si0 _2, 0.6 M .-% CaO and 0.4 M .-% A1 ₂ 0 ₃ + Fe ₂ 0 ₃ + MnO ,

Burnt magnesia spinel stone based on sintered magnesia with 89.5% by weight of MgO and 10.5% by weight of A1 ₂ 0 ₃ .

Burnt magnesia-hercynite stone based sintered magnesia with 91.8 M .-% MgO, 3.4 M .-% A1 ₂ 0 ₃ , 3.8 M .-% Fe ₂ 0 ₃ , 0.7 M .-% CaO and 0.3 mass% Si0 ₂ .

Table 2 The sintered magnesia used for the stones S-0, S-1, S-2 and S-3 had a MgO content of> 97 M .-%. The silicon carbide used had a purity of about 95 M. -%.

The property values mentioned in the table were determined according to the following methods:

Young's modulus: As described in the reference cited in "Review of Scientific Instruments" (1997). In the exemplary embodiment, the modulus of elasticity was determined using an RFDA (Resonant Frequency and Damping Analyzer) from IMCE n.v. , Slingerweg 52, B-3600 Genk.

 Breaking Work, Nominal Notch Tensile Strength, and Characteristic Length: Determined by performing and evaluating a wedge-gap test according to the reference cited above in "CFI Ceramic Forum International" (2007).

Claims

P at a nce r e c h e Composition refractory ceramic offset  a) 75-98 M .-% of at least one basic basic material from the group: sintered magnesia, fused magnesia,  b) 2-25% by weight of at least one granular aggregate of the group: silicon carbide, silicon nitride, silicon oxycarbide, silicon oxo carbonitride,  c) maximum 5% by mass of other ingredients,  in each case based on the total offset. Refractory ceramic offset according to claim 1, the basic basic material of which is> 10 to <40% by mass in one Flour fraction <125μιη present, based on the total offset. Refractory ceramic batch according to claim 1, the basic material of which is> 35M .-% in a grain fraction> lmm, based on the total offset. 4. Refractory ceramic offset according to claim 1, the granular aggregate is present in a grain fraction> 125 μιη and <3mm. 5. Refractory ceramic offset according to claim 1, the granular aggregate is present in a grain fraction> 0.5 mm and <2 mm. 6. Refractory ceramic offset according to claim 1, the granular aggregate in an amount of 2- 1 0 M. -%, Based on the  Total offset, present. 7. Refractory ceramic offset according to claim 1, whose  basic material of at least 95 M -% consists of MgO. 8. Refractory ceramic batch according to claim 1, wherein the dcio value of the basic basic basic material without the  Flour fraction is above the dgo value of the granular aggregate. 9. Refractory ceramic offset according to claim 1, whose Basic basic material has an iron content, measured as Fe ₂ 0 ₃ , of less than 0.6 M .-%, based on the basic base material. The refractory ceramic batch of claim 1 containing less than 0.3% by weight of alumina based on total offset. A refractory ceramic batch according to claim 1 containing less than 0.3% chromium oxide by total offset. 12. Refractory ceramic offset according to claim 1, the granular aggregate contains a maximum of 5M .-% other ingredients, based on the mass fraction of the aggregate in the total offset. .Fire-resistant ceramic stone, prepared from an offset according to claim 1 after pressing and firing at temperatures between 1400 ° C and 1600 ° C, wherein the granular aggregate is a maximum of half sintered with the surrounding basic base material. 14. Refractory ceramic stone according to claim 13 having at least one of the following property values: a) Young's modulus: <60 GPa  b) Breaking work:> 200 N / m  c) nominal notched tensile strength: <9 MPa  d) characteristic length:> 250mm  e) Invariant point:> 1700 ° C